Project Summary While Streptococcus mutans is often cited as the primary etiologic agent of dental caries, evidence that caries is a polymicrobial and ecological disease continues to mount. A detailed understanding of the spatial relationship and functional interaction between S. mutans and its neighbors within the dental plaque community, as well as their impact on disease etiology is still lacking, and one of the unsolved mysteries in cariology is that, while the levels of S. mutans correlate well with the disease incidences overall, there are numerous cases in which an individual has a significant burden of S. mutans, but an absence of disease. Based upon preliminary data indicating that the microbial profile of the dental plaque of healthy subjects was significantly different from that of individuals with caries, we hypothesize that the bacterial species with direct physical interaction with S. mutans within the dental plaque consortium play a critical role in modulating the physiology and pathogenicity of S. mutans. To test this hypothesis, we will carry out three interconnected aims: Aim 1: Developing a systematic approach to discover and characterize the physically interacting partners of S. mutans in a diverse dental plaque community. Three assays will be developed to determine the dental plaque species with which S. mutans physically interacts and explore the biogeography of these interactions. Aim 2: Analyzing oral microbial samples from human subjects with different caries severity and identifying the physically interacting partner species of S. mutans. Clinical samples from individuals with a high S. mutans burden and either advanced dental caries or no disease will be analyzed by the techniques developed in Aim 1, to identify how the S. mutans interacting partners and their spatial relationship within clinical dental plaque differs between the two clinical groups. Aim 3: Investigating the impact of physically interacting partners on S. mutans physiology and pathogenicity. Transcriptomic and metabolomic studies will be used to monitor the impact of interactions with specific partner species on expression of genes involved in the pathogenesis of S. mutans. This study will identify the ecological fingerprints of cariogenic plaque and will greatly increase the understanding of the relationship between S. mutans and its neighbors in the dental plaque community and will also pave the way for the future study of specific S. mutans genes involved in community pathogenicity.